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authorMatt Fleming <matt.fleming@intel.com>2013-10-04 09:36:56 +0100
committerMatt Fleming <matt.fleming@intel.com>2013-10-28 18:09:58 +0000
commit72548e836b0c4abbb652e791dee9c91203a9a4c6 (patch)
tree2eead15738f173ed08ecbedc88adbb0bf2937022 /Documentation/kernel-parameters.txt
parentc158c3bf59951bbb44bd7ccca9e6665dfd1617c5 (diff)
x86/efi: Add EFI framebuffer earlyprintk support
It's incredibly difficult to diagnose early EFI boot issues without special hardware because earlyprintk=vga doesn't work on EFI systems. Add support for writing to the EFI framebuffer, via earlyprintk=efi, which will actually give users a chance of providing debug output. Cc: H. Peter Anvin <hpa@zytor.com> Acked-by: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Jones <pjones@redhat.com> Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Diffstat (limited to 'Documentation/kernel-parameters.txt')
-rw-r--r--Documentation/kernel-parameters.txt8
1 files changed, 5 insertions, 3 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7f9d4f53882c..7a0f202d482e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -792,6 +792,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
earlyprintk= [X86,SH,BLACKFIN,ARM]
earlyprintk=vga
+ earlyprintk=efi
earlyprintk=xen
earlyprintk=serial[,ttySn[,baudrate]]
earlyprintk=serial[,0x...[,baudrate]]
@@ -805,7 +806,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Append ",keep" to not disable it when the real console
takes over.
- Only vga or serial or usb debug port at a time.
+ Only one of vga, efi, serial, or usb debug port can
+ be used at a time.
Currently only ttyS0 and ttyS1 may be specified by
name. Other I/O ports may be explicitly specified
@@ -819,8 +821,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Interaction with the standard serial driver is not
very good.
- The VGA output is eventually overwritten by the real
- console.
+ The VGA and EFI output is eventually overwritten by
+ the real console.
The xen output can only be used by Xen PV guests.